A slime mold is a single-celled organism that can grow on your grass and spreads through spores. It looks like a fungal lawn disease, but it isn’t a true fungus, and it’s not a disease, either. On lawns, it’s sometimes called “dog vomit fungus” – which gives you a pretty clear idea of what it looks like.
Spore masses appear on grass blades as slimy circular or irregular-shaped patches. They typically have a diameter of 4 to 8 inches. Slime molds may be yellow, white, gray, purple, black, or brown. They can also appear as a crusty black, gray, or orange substance on grass blades.
Besides being unsightly, these uninvited lawn visitors’ only fault is that they cause much ado about nothing. Why? Because slime molds are not a plant pathogen. They are rarely harmful to your lawn, and they disappear on their own after a few days. If they don’t, raking, mowing, or hitting them with a powerful jet of water will send them on their way.
Want to learn more? Keep reading to find out how to get rid of slime mold on grass, what this stuff is anyway, and some things you probably never wanted to know about slime mold.
What is slime mold?
The good news is that slime mold is not itself a disease, nor does it cause lawn disease in turfgrass. Slime molds are single-celled organisms that use grass stems and leaves as structural support for their reproductive spore masses and when individual spores clump together to search for food.
Slime mold has a variety of species, and many of them produce individual fruiting bodies, also called sporangia or spores. Thousands of fruiting bodies, which are approximately the size of a pinhead, invade leaf surfaces. They join together and form irregular patches or little circles on turfgrass leaves. These blobs of clumped-together fruiting bodies, called plasmodium (slime mold), make the grass look greasy or slimy.
The fruiting bodies eventually turn crustlike. When the crust disintegrates, the mass of spores is dispersed by foot traffic, water, wind, and mowers. The spores germinate and become the plasmodium (the slimy, oily blobs) you see on the grass after many days of overcast, wet weather.
Slime molds are rarely harmful and can be good for your lawn. They are saprophytes, meaning they break down organic material by feeding on decaying and dead organic matter. This can be good for your lawn because, as slime molds break down this matter, they eat away plant pathogens and bacteria that could be harmful to your lawn.
However, the slimy gray, white, and purple spore masses on turfgrass leaves are unsightly, and homeowners in pursuit of pristine lawns are not big fans.
How to get rid of slime mold on grass
You may not want to be greeted by slime mold when you walk out of your house, but luckily, it will disintegrate in a week or less, all on its own. So, homeowners can skip the chemical or synthetic control measures to get rid of this sticky, unsightly material on their lawns.
If you do not want to wait for it to disappear on its own, you can remove it from grass leaf surfaces very easily with manual means. Some ideas:
- Scoop it off with a shovel
- Hit the grass with a powerful stream of water
- Rake it off the grass
- Dethatch the lawn
- Mow the lawn
If slime mold repeatedly appears in lawn areas with poor drainage or heavy thatch, you can renovate the affected areas to reduce the occurrence of the slimy blobs.
Fungicides are ineffective at stopping the mass of spores from developing on grass, and they are not suggested for home lawns. They can harm beneficial organisms and the environment. Fungicides are actually worse for your lawn’s health than the harmless slime mold itself.
How to spot slime mold
As stated previously, different varieties of slime mold look different:
- Physarum looks like brightly colored slime blobs and usually only retains the bright color for a few days before turning dark, which typically means the mold has dried and now has a powdery texture.
- Mucilago is described as resembling dog vomit and is more commonly referred to as “dog sick fungus” or “dog vomit fungus.” It is a yellow-to-white color and is one of the larger species.
- Fuligo is also said to look like dog vomit or scrambled eggs when it is on mulch or turfgrass.
You may see a purple, irregularly shaped blob that looks like it is the start of something in a sci-fi horror movie – something that will get much bigger and scarier. It doesn’t help that the blobby substance can show up overnight. Or, from a distance, it may just look like a child dropped her silly putty in the grass.
In general, young spores are sticky, but they dry to a dark-colored, powdery substance. They can be wiped or rubbed off when they are dry.
Slime mold may turn your grass leaf blades slightly yellow because the mold prevents photosynthesis. But no worries, the grass will eventually rebound from the effects, especially since slime mold goes away so quickly.
Causes of slime mold
When organic matter builds up in the grass, it can cause slime mold to develop. Extensive thatch and poor drainage can make the problem worse. Grass that stays wet too long can result in slime mold growing overnight.
Slime mold is common when the weather is wet and warm. Damp soil and insufficient sunlight can also encourage slime mold growth.
Warm regions of the country are prone to slime mold, especially when the area has experienced heavy rain. Fortunately, slime mold disintegrates on its own when the grass dries.
The fruiting bodies leave behind slime mold spores that produce more of the organism. The mold mostly reoccurs on home lawns with poor drainage, lots of shade, or thick thatch build-up.
How to prevent slime mold
Although slime mold forms naturally in its preferred environment of warm, wet weather, there are some things you can do to reduce your chances of sharing your yard with this unappealing blob of stickiness. As with most lawn care problems, the best treatment for slime mold is prevention. Many of the prevention strategies are the same as the treatment techniques.
Organic matter accumulation promotes slime mold, so the key is to do things regularly that reduce build-up. Raking up debris, like grass clippings, mowing regularly, and decreasing thatch accumulation will reduce organic matter pile-up. You can keep thatch in check by dethatching the lawn once a year.
Do not overwater your grass, as this contributes to slime mold growth. Learn proper lawn watering techniques in our article, When and How to Water Your Lawn.
Give your lawn as much sunlight as possible. While you cannot control the direction of the sun or move your grass around so that it is hit by sunrays, you can prune trees and shrubs to minimize sun blockage.
More about slime mold
Most slime mold found on grass belongs to the subfamilies Physarum cinerum, Mucilago crustacea, and Fuligo septica. Slime mold is a primitive organism. It has been both classified and not classified as a plant, animal, or fungi. Confusing? Yes, I know. Slime mold has characteristics of both fungi and amoebae.
Surely, you remember amoebae from your grade-school science class. They are single-celled organisms. What you may not remember is that they reproduce by spores. They are asexual and divide themselves into new cells to reproduce.
In case you wanted to know, slime mold is a heterotroph – whatever that means. (Here comes the more than you ever wanted to know part.)
Heterotrophs are organisms that get nutrients and energy by eating other animals or plants. I’m sure, by now, you’re thinking like me. Aren’t humans heterotrophs, too? That’s right! You have some common ground with the slimy little organisms covering your lawn!
FAQ about slime mold on grass
No. Although slime mold may be disgusting-looking – or maybe even intriguing to some (to each his own) – it is not dangerous to humans or pets.
Physarum is one of the most common varieties of slime mold found in turfgrass.
Dry weather is one of the best times to remove slime mold by raking it. But even better, it will usually disappear on its own when the weather is hot and dry.
Final Thoughts
A little slime mold won’t hurt you or your lawn. It may even be good for your yard. The mold consumes plant pathogens and bacteria that can be harmful to plants and grass.
Fortunately, slime mold is easily removed. Be mindful that using fungicides to treat this organism is unnecessary and strongly advised against. For that reason, if you feel you must use fungicides to get rid of slime mold, you may want to call a professional first.
Slime mold can be mistaken for pests or fungi that are lawn diseases, and you want to make sure you have identified the culprit properly for appropriate treatment.
At the end of the day, no worries. You don’t have to possess the horticulture skills or plant pathology know-how to deal with this silly-putty imposter. Let Lawn Love connect you with lawn care professionals in your area to handle all of your lawn care tasks, including helping you get rid of and prevent the return of the infamous slime mold.
Main Photo Credit: Juan Francisco Moreno Gamez | Canva Pro | License
